help wanted for this rookie

[umper]

Can anyone remember their first year umpiring for giving advice? I did my 2nd and 3rd games today with the little guys (10 and 11yrs.)
I had three close plays on the bases and all three calls went against one particular team. I really start second guessing my call when the coaches are rambling on about how it wasn't even close.
This leads me to the question. How do you prepare to make that bang-bang call at first? What are your eyes watching for?